In the context of the integration of devices for microelectronics, microbatteries have the advantage of being capable of adapting to the increasing needs of such applications in terms of voltage and power. Such an adaptation often requires assemblies of single microbatteries by series and/or parallel connection methods.
Thus, a series assembly provides the possibility of modulating the output voltage while a parallel assembly enables to substantially increase the total capacity.
To meet this request, many assembly solutions have been developed.
For example, document U.S. Pat. No. 6,982,132 describes a method of monolithically stacking microbatteries by successive depositions of the active layers (electrodes and electrolyte) on the same substrate. However, this method does not enable to integrate these microbatteries with external circuits due to the absence of electric contacting areas.
Document WO 2009/073150 describes a method of stacking and bonding two single microbatteries positioned on each other. The electric continuity is provided by means of microvias crossing one of the substrates to interconnect the current collectors of the two microbatteries. However, forming and filling the microvias without altering the microbattery performances turn out being very delicate processes. Such difficulties become insuperable when the number of microbatteries to be stacked increases.
It further remains essential to efficiently protect the reactive lithium-based components against oxidizing species particularly oxygen, nitrogen, and water vapor.
Thus, the main difficulty of a “vertical” assembly lies in the forming of specific electric contacts without short-circuiting the lithium microbatteries, while maintaining a mechanical robustness of the sides, as well as a resistance towards oxidization.
To solve these problems, an additional technically-burdensome encapsulation step is sometimes necessary to ensure a robust and complete protection of all the active layers of the oxidizing species.